The invention relates generally to a ring channel blower, also known as a side channel blower or lateral duct fan, that is intended, in particular, for combustion air conveyance in heaters, such as motor vehicle heaters. More specifically, the invention is directed to a ring channel blower that has a ring channel formed in a housing part that has an inlet opening and a discharge opening as well as a cross piece-shaped interrupter lying between them, and a rotatable impeller with vanes whose edges face the ring channel.
A ring channel blower of the type mentioned above is known from U.S. Pat. No. 4,749,338. The cross piece-shaped interrupter between the inlet opening and the discharge opening in this ring channel blower is bounded by two boundary edges that run approximately parallel to each other, are made there as straight lines and run approximately in the direction of the diameter of the ring channel. It has been shown that such a ring channel blower operates relatively noisily, which is increasingly felt to be especially inconvenient when, corresponding to current efforts by motor vehicle producers, the passenger compartment is becoming more quiet by soundproofing. Especially with the use of such a ring channel blower in a motor vehicle heater, its operation can be perceived in the passenger compartment of the motor vehicle. This can essentially be ascribed to the fact that the abrupt transition from the essentially straight boundary edges of the interrupter to the discharge opening and/or to the inlet opening, produces flow noises that have frequencies in the audible range.
Also known (from German Offenlegungsschrift No. 25 31 740 and corresponding U.K. Application No. 2,104,959) is a ring channel blower with a cross piece-shaped interrupter having nonuniform boundary edges which progressively uncover/cover the ring channel at the inlet/discharge areas via sections which taper toward the middle of the ring channel in a direction downstream/upstream relative to the inlet/outlet of the ring channel and which may have a V-shaped central notching at the free ends thereof. While producing somewhat less abrupt transitions, such a blower also operates relatively noisily. The same is also true for the V shape of the boundary edges of U.S. Pat. No. 4,412,781 and the concave shape shown in Japanese Patent Publication No. 56-594, both of these blowers requiring noise suppressing mufflers.